1. Field of the Invention
The present invention relates generally to semiconductor processing and, more specifically, the present invention relates to preparing a plurality of dice from a semiconductor wafer.
2. Background Information
A variety of products may be fabricated from semiconductor wafers such as for example integrated circuits, optical devices, etc. A plurality of dice are typically arranged on a wafer when fabricated and then the dice are eventually separated into individual dice at some point during the process. For optical devices, additional processing steps are typically involved.
For example, after an optical device wafer is finished processing, each die usually must undergo several more steps before it can be packaged or tested. The first step is to liberate each die by dicing up the wafer. Dicing has a serious issue in that it can cause chipping of the die, which can destroy optical waveguides on the die. It also leaves the facets of the waveguide too rough to adequately pass light.
Next the die is removed from the wafer and the edges of the die that are perpendicular to the waveguides are polished. The reason for the polish is to obtain an optically smooth surface at the inputs and outputs of the optical waveguides. These interfaces must be smooth, as any roughness will contribute to the optical loss of the device. Mechanical polishing has several major drawbacks. The first is that it is very time consuming, typically taking anywhere from 1-3 hours to polish a single die. Also, the polishing exerts a force on the optical waveguides that can cause them to chip or break, causing the yield of devices per die to decrease.
Once polished the die are manually cleaned. This is another step that can cause the optical waveguides to chip or break. It is also difficult to determine if the optical waveguides are truly clean as they are on the order of only a few microns. A microscope could be used to examine each and every waveguide, however, the throughput time would become astronomical as there are typically many optical waveguides on a single die.
In some instances, the devices are then anti-reflection (AR) coated to reduce reflections at the inputs and outputs of optical waveguides due to their interface with air. If the devices are not properly cleaned, the AR coating will not stick. If the AR coating does not stick, not only will the AR coating not help in reducing the reflectivity, but the lack of the AR coating sticking may also induce optical scattering which will cause the optical loss to be higher than if the AR coating wasn't there at all.